This invention relates to a system and method for calibrating a vehicle odometer, and specifically to a system and method for automatically calibrating an odometer.
Typically, an odometer of a vehicle senses the distance traveled by the vehicle to record mileage and determine vehicle speed. Public transportation vehicles record and track mileage for budget purposes and to evaluate driver performance. Mileage information is also used to coordinate and initiate arrival and departure announcements. If the distance traveled is not accurately measured, announcements may be timed improperly, and resources may be improperly allocated.
Typically, a conventional odometer includes a series of gears connected by a rotating cable to a rotating mechanism of the vehicle such as a tire, transmission or engine component. The cable in turn rotates a series of gears correlated to relate rotation of the cable to distance traveled by the vehicle. A known improvement over mechanical linkage includes an electronic sensor that emits a number of pulses for each rotation of a wheel, engine or transmission component. The pulses obtained from the sensor are calibrated to represent a known distance. Calibration of the odometer relates the number of pulses to distance in which the vehicle has traveled within a predetermined tolerance.
A known calibration method includes driving the vehicle along a preset path of a known distance and recording the number of pulses relative to that known distance. Variations in vehicle speed and the path driven create inaccuracies to the calibration. Re-calibration is required whenever maintenance is performed on the vehicle to assure accuracy of the odometer.
Many factors can change the calibration of an odometer. Factors that effect the calibration of the odometer include vehicle weight; tire pressure, and environmental conditions. In addition, when the tires of a vehicle are changed, the characteristics of the vehicle change requiring a new calibration to assure accuracy.
A known calibration method improvement includes the use of signals generated from a global positioning satellite to determine the distance traveled of the vehicle. A global positioning receiver disposed within the vehicle receives signals from the global positioning satellite that are used to determine the precise distance in which the vehicle has traveled. The precise distance in which the vehicle has traveled is then used with corresponding pulse data received from sensors onboard the vehicle. The sensors onboard the vehicle record pulses indicative of movement of the vehicle.
However, the vehicle must be traveling at a constant speed to provide an accurate determination of the number of pulses received relative to the distance traveled. It is known to apply statistical methods to account for the inaccuracies caused by variations in speed during calibration. However, such methods are complex and memory intensive. Further, such statistical methods only reduce the magnitude of inaccuracies caused by variations in speed.
Accordingly, it is desirable to develop a system and method for accurately calibrating an odometer by eliminating the use of aberrant data caused by vehicle speed variations.
An embodiment of this invention is a system and method for automatically calibrating a vehicle odometer by collecting vehicle speed data for odometer calibration only when the vehicle is traveling at a constant speed.
The system includes a sensor transmitting a series of pulses indicative of movement of the vehicle to a vehicle controller. The vehicle controller also receives signals indicative of a distance traveled of the vehicle from a receiver. The receiver receives signals emitted from a global positioning satellite indicative of current vehicle position. Receiving several signals of the current instantaneous position of the vehicle allows the determination of the distance traveled by the vehicle. The controller records a number of samples comprising a number of pulses relative to distance traveled. Combining several of the recorded samples provides an average number of pulses relative to distance value. The current calibration of the odometer is reflected in a current number of pulses relative to distance value. The current value is compared to the average value and the odometer calibration is changed to reflect the average value in response to the difference between the two values being greater than a predetermined tolerance.
The method of calibrating an odometer includes the steps of collecting a number of pulses indicative of movement of the vehicle. If the vehicle is above a predetermined minimum speed, a comparison is made between incoming pulses that indicate movement or speed of the vehicle. The comparison of incoming pulses determines if the vehicle is traveling at a constant speed. If the vehicle is traveling at a constant speed, the controller records the number of pulses relative to a distance traveled as a sample. The controller gathers sample data in this manner until recording a sufficient number of samples. The average number of pulses relative to distance value represents a number of pulses relative to distance traveled for current operating conditions of the vehicle. The average and current number of pulses relative to distance are compared, and if there is a sufficient difference, the calibration of the odometer is updated accordingly.
Calibration of the odometer can change for many different reasons including environmental conditions, tire pressure increase or decrease, change of tire size, additional A vehicle load, and any number of considerations that can combine to change the operating characteristics of the vehicle. For this reason, data samples are continually gathered and compared to the current calibration of the odometer. By continuously operating to update the calibration value of the odometer, the accuracy of the odometer reading can be ensured for a vehicle throughout operation.